With the recent development of information communication technology, a variety of wireless communication techniques are being developed. From among them, a WLAN is technology for wirelessly accessing the Internet at homes or companies or in specific service providing areas by using portable terminals, such as a Personal Digital Assistant (PDA), a laptop computer, and a Portable Multimedia Player (PMP), based on radio frequency technology.
In order to overcome limitations to the communication speed that was considered as being weakness in a WLAN, an IEEE 802.11n standard has recently been established as a technology standard. An object of the IEEE 802.11n standard is to increase the speed and reliability of a network and to extend the coverage of a wireless network. More particularly, in order to support a High Throughput (HT) having a maximum data processing speed of 540 Mbps or higher, minimize an error in transmission, and optimize the data rate, the IEEE 802.11n standard is based on Multiple Inputs and Multiple Outputs (MIMO) technology using multiple antennas on both sides of a transmitter and a receiver.
As the WLAN is actively propagated and applications employing the WLAN are diversified, a necessity for a new WLAN system for supporting a throughput higher than the data processing speed supported by the IEEE 802.11n standard is on the rise. The next-generation WLAN system supporting a Very High Throughput (VHT) is a next version of the IEEE 802.11n WLAN system and is one of IEEE 802.11 WLAN systems which have recently been newly proposed in order to support a data processing speed of 1 Gbps or higher in a MAC Service Access Point (SAP).
The next-generation WLAN system supports transmission using a Multiple User-Multiple Input Multiple Output (MU-MIMO) scheme in which a plurality of non-Access Point Stations (AP STAs) accesses a radio channel at the same time in order to efficiently use the radio channel. According to the MU-MIMO transmission scheme, an AP can transmit a frame to one or more MIMO-paired STAs at the same time.
When an AP transmits data to a plurality of destination STAs on a plurality of spatial streams according to the MU-MIMO scheme, the plurality of destination STAs may have different capabilities. In other words, a supportable bandwidth, a Modulation Coding Scheme (MCS), Forward Error Correction (FEC), etc. may differ depending on a type, an object, a channel environment, etc. of an STA.
According to the MU-MIMO transmission scheme, an MU-MIMO transmitter (AP) can transmit data to each of a plurality of MU-MIMO-paired receivers through at least one spatial stream. Here, a channel between the transmitter and a first receiver and a channel between the transmitter and a second receiver may have mutual interference. Interference between the channels between the transmitter and the receiver may hinder normal data transmission and reception as described above, which may deteriorate the overall throughput of a WLAN system. In order to improve the throughput in a WLAN system supporting the MU-MIMO transmission scheme, a sequentially optimized and recommended Modulation and Coding Scheme (MCS) needs to be fed back by taking interference between different channels into consideration when data is transmitted. A method of an AP transmitting control information to an STA that has been requested to transmit a Modulation and Coding Scheme (MCS) feedback (MFB) so that the STA can calculate an optimized MCS value when calculating and feeding back a recommended MCS value and a method of efficiently transmitting supplementary information according to a type of an MFB when an STA transmits the MFB to an AP need to be taken into consideration.